Intravenous administration sets are generally used to infuse various types of solutions into a patient. A set provides a means of controlling the sterile passage of a physiological liquid (e.g. saline, glucose solution etc) from a rigid or flexible supply container into a patient. Conventional intravenous administration sets feature a closed chamber with a nozzle, creating drops when the liquid flows. The purpose of this is to enable the liquid flow rate to be calculated by counting the number of drops per unit time. This can be time consuming and inaccurate, as drop size is not constant, and the conversion of drop timing to liquid flow rate can be difficult.
A number of well established flow meter designs have been adapted for use in intravenous liquid administration.
Variations on the rotameter design (e.g. U.S. Pat. No. 3,587,313) employ a small ball of proper specific gravity (usually greater than the liquid, though it may also be a float in some designs) positioned within a tapered vertical tube. The ball is pushed towards the larger cross sectional area of the indicating tube as the liquid flows; the position of the ball is indicative of the liquid flow rate. Though these devices enable more accurate regulation and adjustment of flow rate, they are expensive to manufacture due to the high tolerances required, as well as the potentially complex assembly of components.
Another type of flow meter device (U.S. Pat. No. 2,479,786A) employs a tube arranged vertically, with the liquid inlet at the top, and with a short portion bent back upon itself. A small orifice in the wall of the tube at the bend allows liquid to flow downwards. This arrangement is encased within a larger sealed container having an outlet to further tubing leading to the patient. Liquid flow in the tube, combined with the resistance to flow caused by the orifice, causes the liquid level in the shorter portion to rise to a level proportional to the flow rate. This design is simpler than the rotameter variants, but is inaccurate at low flow rates, and it is difficult to manufacture multiple units with consistent geometry, further affecting calibration and accuracy.
Another type of flow meter device (U.S. Pat. No. 4,136,692A) uses a similar principle, replacing the bent tube with two connected tubes within a larger sealed tube with an outlet to the patient. The small orifice in U.S. Pat. No. 2,479,786A is replaced with highly accurate orifice disks of minimal thickness (0.001 in). This has the effect of minimising any effects of changing temperature and viscosity on accuracy, but the design remains a relatively complex assembly of small parts, resulting in manufacturing costs higher than a standard liquid administration set.
Accordingly, the primary objective of the present invention is to provide a flow meter device that is easier, quicker, and more accurate to use than the standard administration set that requires the counting of drops, and is comparable in cost to manufacture.